Rhotekin regulates axon regeneration through the talin–Vinculin–Vinexin axis in Caenorhabditis elegans.

Axon regeneration requires actomyosin interaction, which generates contractile force and pulls the regenerating axon forward. In Caenorhabditis elegans, TLN-1/talin promotes axon regeneration through multiple down-stream events. One is the activation of the PAT-3/integrin–RHO-1/RhoA GTPase–LET-502/ROCK (Rho-associated coiled-coil kinase)–regulatory non-muscle myosin light-chain (MLC) phosphorylation signaling pathway, which is dependent on the MLC scaffolding protein ALP-1/ALP-Enigma. The other is mediated by the F-actin-binding protein DEB-1/vinculin and is independent of the MLC phosphorylation pathway. In this study, we identified the svh-7/rtkn-1 gene, encoding a homolog of the RhoA-binding protein Rhotekin, as a regulator of axon regeneration in motor neurons. However, we found that RTKN-1 does not function in the RhoA–ROCK–MLC phosphorylation pathway in the regulation of axon regeneration. We show that RTKN-1 interacts with ALP-1 and the vinculin-binding protein SORB-1/vinexin, and that SORB-1 acts with DEB-1 to promote axon regeneration. Thus, RTKN-1 links the DEB-1–SORB-1 complex to ALP-1 and physically connects phosphorylated MLC on ALP-1 to the actin cytoskeleton. These results suggest that TLN-1 signaling pathways coordinate MLC phosphorylation and recruitment of phosphorylated MLC to the actin cytoskeleton during axon regeneration. Author summary: Axon regeneration requires actomyosin interactions, whereby actomyosin generates contractile forces to advance the regenerating axon. In C. elegans, TLN-1/talin promotes axon regeneration through the PAT-3/integrin–RHO-1/RhoA–LET-502/ROCK–MLC phosphorylation signaling pathway, which is dependent on the MLC phosphorylation scaffold protein ALP-1/ALP-Enigma. TLN-1 also activates the F-actin-binding protein DEB-1/vinculin in axon regeneration, but this pathway activates SORB-1/vinexin but does not induce MLC phosphorylation. Here, we identified the svh-7/rtkn-1 gene, which encodes a homolog of the RhoA-binding protein Rhotekin, as a regulator of axon regeneration. However, we show that RTKN-1 does not function in the RhoA–ROCK–MLC phosphorylation pathway in the regulation of axon regeneration. Instead, RTKN-1 can connect phosphorylated MLC on ALP-1 to the actin cytoskeleton by physically linking the DEB-1–SORB-1 complex to ALP-1. This study suggests that the TLN-1–DEB-1–SORB-1–RTKN-1 axis promotes axon regeneration by recruiting myosin to the actin cytoskeleton via ALP-1. [ABSTRACT FROM AUTHOR]